1. Field of the Invention
The present invention relates to a flow separation reducer for preventing an airflow from being separated from an aircraft surface region where turbulent and separated flows tend to occur, such as at a joint between a main wing and an engine nacelle.
2. Description of the Related Art
On aircrafts with engines mounted on main wings, airflows produced by engine nacelles and the main wings interfere with each other at joints where they are coupled to each other, producing different flow patterns from those which would be generated by the engine nacelles and the main wings if they were separate and independent from each other. Such a phenomenon is refereed to as flow interference. One known attempt to suppress separated flows in flow interference regions has been to use fillets or the like which provide smooth surfaces at the joints between the engine nacelles and the main wings.
According to a structure for preventing an airflow from being separated, a small vortex generator is mounted on an upper surface of a main wing, for example, for dispersing a boundary layer prior to being separated thereby to delay the separation of the flow.
U.S. Pat. No. 4,540,143 discloses a wake control device mounted on an upper surface of an engine nacelle supported on a main wing for shedding a strong vortex which prevents a nacelle wake from spreading over the upper surface of the main wing.
Vortex control devices are revealed in U.S. Pat. Nos. 4,685,643 and 4,884,772, and liftvanes are shown in U.S. Pat. No. 3,744,745.
The use of fillets which provide smooth surfaces at the joints between the engine nacelles and the main wings is effective in regions where violent turbulent and separated flows are produced. However, since the fillets increase the frontal area of the engine nacelle and main wing combination, they also increase the aerodynamic drag thereof. Furthermore, the application of a fillet to an existing aircraft structure would need a substantial modification of the aircraft structure. For these reasons, it has not been an easy and simple choice to use fillets to prevent flow separation.
Vortex generators can relatively easily be installed on existing aircraft structures. The vortex generators are, however, comparatively ineffective and incapable of preventing flow separation in regions of very violent flow.